Protective immunity to viral infection requires a complex set of effector responses mediated by multiple cell types. The anti-viral effector functions mediated by T cells include cytolysis, cytokine production, and help for antibody production. To achieve the required magnitude of T cell expansion and the appropriate balance of T cell effector functions depends on the integration of diverse signals impinging on the T cell. One critical component of this process is the biochemical signaling pathways involved in transducing receptor signals leading to changes in gene transcription. While many of the intracellular molecules involved in these pathways have been identified, and their roles in T cell signaling characterized at the biochemical level, much less is known about the functions of these molecules in distinct in vivo immune responses. The goal of this proposal is to address the role of Tec kinases, Itk and RIk, and Tec kinase-dependent signaling pathways, in anti-viral T cell-mediated immunity. Preliminary data indicate that Itk-deficient and Itk/RIk deficient mice have impaired responses to LCMV infection by both CD4+ and CD8+ T cells. As these Tec kinases are known to play a critical role in TCR signaling leading to the activation of phospholipase C-g1, we hypothesize that the absence of Irk, or Itk and RIk, leads to poor T cell expansion, reduced differentiation of effector T cells, and impaired cytokine production in response to LCMV infection. We also hypothesize that these deficiencies will be observed in response to both non-cytopathic (e.g., LCMV) as well as cytopathic (e.g., vaccinia virus) viral infections. To address these hypotheses, we propose to dissect the underlying mechanism(s) responsible for defective T cell responses to viral infection by Tec kinase-deficient T cells. We will use a combination of MHC-peptide tetramers, adoptive transfers of marked T cells, intracellular cytokine analysis, and quantitative gene expression analysis to assess each component of the anti-viral response, both in the acute and the memory phase. These experiments will be complemented by global gene expression profiling to identify genes with aberrant expression patterns in Itk-/- or Itk-/-RIk-/-T cells during the anti-viral response. These studies will provide important information for future efforts to modulate T cell immune responses in vivo by manipulating distinct T cell signaling pathways.